chrisnelsoncentare/jquery-mobile-datebox — comment on commit 883f0f6f49f3809e7c7eaad63af54829fea8f7d5
File: js/jquery.mobile.datebox.js line 2169
By chrisnelsoncentare:

The logic above is what was causing the issues I saw. Previously, there was code to adjust the popup from being fully centered over the input, if that would result in the top/bottom being off screen. I noticed the logic didn't account for headers/footers (and my site uses the new fixed approach in the 1.1 nightly builds) so this code adjusts in the event a header/footer is present.